It is currently known that metal ions such as silver ion (Ag+), zinc ion (Zn2+) and divalent copper ion (Cu2+) suppress proliferation of microorganisms, or germicidally act against microorganisms. There have been developed variety kinds of antimicrobial materials consisting of these metal ions carried on a substance such as zeolite and silica gel, antimicrobial materials consisting of a combination with titanium oxide having a photocatalytic action, and the like.
As for the antimicrobial action or antiviral action of divalent copper ion, there have been elucidated actions of changing structures of cell membranes and destroying functions of the same (Progress in Medicinal Chemistry, 31, pp. 351-370, 1994) and action of denaturing nucleic acids (CRC Critical Rev. Environ. Cont., 18, pp. 295-315, 1989), and as for the action of divalent copper ion against viruses, there are reports by Sangripanti et al. (Appl. Environ. Microbiol., 58, pp. 3157-3162, 1992; Appl. Environ. Microbiol., 59, pp. 4374-4376, 1993; AIDS Res. Hum. Retrovir., 12, pp. 333-336, 1996; Antimicrob. Agent Chemother., 41, pp. 812-817, 1997). It has also been reported that a material having a glass surface coated with a thin film of copper(II) oxide (CuO) or a thin film containing CuO together with titanium oxide (TiO2) had phage inactivating actions in a T4 phage experimental system (virus inactivation model) (Appl. Microbiol. Biotechnol., 79, pp. 127-133, 2008).
Although almost no reports have so far been made as for antimicrobial action of monovalent copper compounds, it has been reported that the antibacterial activity (MBC) of the monovalent copper compound (Cu2O) against bacteria such as methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, and Pseudomonas aeruginosa is inferior to that of divalent copper compound (CuO) or metallic copper (Cu), and remarkably weaker than that of silver (Ag) (International Journal of Antimicrobial Agents, 33, pp. 587-590, 2009, especially p. 589, Table 1). Further, there is also a report about differences in antibacterial activities of cuprous oxide due to the crystal polymorphism thereof (Chem. Commun., pp. 1076-1078, 2009), and bacteriostatic actions (MIC) against Bacillus bacteria, Staphylococcus aureus, Pseudomonas aeruginosa and the like may differ depending on the crystalline forms. However, it has not been reported that antibacterial activity of a monovalent copper compound is especially stronger than that of a divalent copper compound.
As for the antiviral action of a monovalent copper compound, nanoparticles with a mean particle size up to about 500 nm having an antiviral action are disclosed in Japanese Patent Unexamined Publication (KOHYO) No. 2009-526828, and it is explained that the nanoparticles may contain Cu2O in the paragraph [0020] of the patent publication. However, the aforementioned patent publication does not explicitly disclose the antiviral action of Cu2O per se, and those skilled in the art cannot understand whether or not a monovalent copper compound has a virus inactivating action in view of the disclosure of the publication.